1. Field of the Invention
The present indention relates generally to an inorganic composition for low temperature firing, more particularly, to an inorganic composition for use in a multilayered ceramic printed circuit board.
2. Description of the Prior Art
With miniaturizing of the electronic devices, ceramic printed circuit boards have been widely used for various electronic devices. Nowadays, multilayered ceramics have been developed to achieve high integration, and are prepared by forming a circuit pattern on a surface of the ceramic green sheet, laminating several sheets and firing. Alumina has been used as a material of such a multilayered ceramic printed circuit board.
However, alumina has several drawbacks. Since the firing temperature for alumina is as high as 1500 to 1600.degree. C., a large amount of energy is required, thereby inherently causing a high cost. Since the electroconductive material having a high specific resistance for an inner circuit formed in the multilayered printed circuit board is limited to tungsten (W), molybdenum (Mo), or the like, which are not oxides under high firing temperature, the electric resistance of the circuit per se inherently becomes higher. Since the thermal expansion coefficient of alumina is higher than those of a silicon chip which is mounted on the alumina board, thermal stress is imparted to the silicon chip, thereby causing cracks. Since alumina has a dielectric constant as high as about 10, the delay in signal transmission in the circuit becomes longer.
Under the circumstances, the inventors have been studied and developed a ceramic composition for low-temperature firing of multilayered ceramic printed circuit board.
Laid-open Japanese patent application No. 1-246176 discloses a ceramic composition. The method of producing a multilayered ceramic printed circuit board in accordance with the application is as follows: Firstly, cordierite powder, powder of oxides/or compounds of Ca, Sr, or Ba, SiO.sub.2 powder, MgO and Al.sub.2 O.sub.3, and oxides/or compounds of Cr, Fe, Co, Ni or Cu, are weighed and mixed. Then, the mixed material is calcined and crushed into powder. A ceramic slurry is made by adding binder to the powder. Next, a ceramic green sheet is prepared by means of a sheet forming method, for example, the doctor blade method. A plurality of the ceramic green sheets are laminated and sintered to obtain a multilayered ceramic printed circuit board.